Generally, a negative working light sensitive planographic printing plate material is imagewise exposed to harden the exposed portions, dissolving away the unexposed portions, washed with water, and subjected to finisher gumming treatment to obtain a planographic printing plate. In recent years, an attempt has been made in which after digital exposure is made based on image information employing a laser light in order to provide high dissolving power and sharpness, development treatment is carried out to obtain a planographic printing plate. For example, there is a system for preparing a planographic printing plate, in which a light source is modulated based on image information transported from a communication line, or based on output signals from an electronic plate making system or an image processing system, a light sensitive material is directly scanning exposed employing the light source.
There is a problem in a conventional planographic printing plate material employing a diazo resin in that it is difficult to increase sensitivity or to carry out spectral sensitization for meeting an emission wavelength of a laser for digital exposure In order to obtain high sensitivity.
In recent years, as a light sensitive material suitable for laser exposure, which can increase sensitivity and carry out spectral sensitization, a planographic printing plate material has been noted which comprises a photopolymerizable light sensitive layer containing a photopolymerization initiator. However, a planographic printing plate material for CTP (Computer To Plate) for recording a digital image according to laser-exposure is generally poor in printing durability. A printing plate material with high printing durability has been desired in various printing industries such as newspaper printing or commercial printing industries.
In order to obtain high sensitivity, a method of employing a photopolymerization has been studied, and a method of employing an s-triazine compound as a photopolymerization initiator has been proposed (see, for example, Japanese Patent O.P.I. Publication Nos. 48-36281, 54-74887, and 64-35548.). However, this method could not provide satisfactory sensitivity. Further, a technique of employing a combination of an iron-arene compound and a peroxide as a photopolymerization initiator has been proposed (see, for example, Japanese Patent O.P.I. Publication No. 59-219307.). However, this technique also could not provide satisfactory sensitivity.
In order to obtain high printing durability, there have been disclosed a technique employing a titanocene compound as a photopolymerization initiator (see Japanese Patent O.P.I. Publication Nos. 2001-209170 and 2001-183822), a technique employing autoagglutination of urethane bond of a urethane resin (see Japanese Patent O.P.I. Publication No. 2001-100412), a technique employing a an ethylenically unsaturated compound containing a phosphate ester bond (see Japanese Patent O.P.I. Publication No. 10-10719), and a technique employing a silane coupling agent or employing a diazonium compound disclosed in Japanese Patent O.P.I. Publication No. 2001-249444. These techniques are not satisfactory, and a method solving the above problems has been desired.
Accordingly, an object of the invention is to provide a light sensitive composition, a light sensitive planographic printing plate material and a manufacturing method of a printing plate, providing high sensitivity and excellent printing durability.